In an integrated circuit device or a discrete semiconductor device, such as a power switch or a load switch, there is a power supply apparatus having two power supply input terminals. Such a power supply apparatus is used for switching and distribution of power between power supply units and a plurality of semiconductor devices. A power supply apparatus in which a negative-channel Metal-Oxide-Semiconductor (nMOS) is used as a switching element is common.
However, a power supply apparatus of the related art in which the nMOS is used as the switching element has the following problems. First, when boosting a bias voltage, a boosted bias voltage must be adjusted so that the voltage level becomes higher than an input voltage by at least the threshold voltage of the switching element. Thus, limitations due to performance of a boosting circuit between the bias voltage and the input voltage may occur. Furthermore, when turning on a switch by applying a voltage to a gate of the nMOS transistor, the gate must generally be driven by a boosting circuit and an oscillation circuit in which current must flow. As a result, current consumption of the power supply apparatus is increased. Then, the power supply apparatus also needs a configuration in which bias and input terminals are connected together in view of a configuration of the circuit and the like depending on a configuration of a power supply system using the power supply apparatus. However, when the input voltage is low, a large boosting capability is needed and current consumption in the power supply apparatus is further increased. Furthermore, in this case, it is often troublesome to obtain a desired boosted voltage within the power supply apparatus.
In the related art, when using the power supply apparatus in which the nMOS transistor is the switching element, power supply devices which are optimized to for their respective needs are required. That is, in the power supply system, if the input terminal and the bias terminal are connected together in some circuit blocks, and the input terminal and the bias terminal are not connected together in other circuit blocks, the same power supply device cannot be used for all the circuit blocks. Furthermore, when the input voltage and the bias voltage vary from time to time, the power supply devices cannot be used.